1. Field of the Invention
The present invention relates to methods for enlarging and placing a hardenable permeable material in a wellbore which penetrates an unstable hydrocarbon producing subterranean zone or formation during drilling.
2. Description of the Prior Art
In the drilling of a wellbore with a rotary drill bit, weight is applied to the drill string (a string of connected drill pipe sections) while the drill bit is rotated. A fluid, often referred to as drilling fluid or drilling mud, is circulated through the drill string, through the drill bit and upwardly to the surface through the annulus between the drill string and the walls of the wellbore. The drilling fluid cools the drill bit, removes cuttings from the wellbore and maintains hydrostatic pressure on pressurized subterranean formations.
During the drilling of a wellbore, the wellbore may penetrate incompetent or otherwise unstable subterranean zones or formations such as unconsolidated sands or shales. Such unstable zones or formations can have very high permeabilities whereby severe drilling fluid losses occur into the zones or formations. Also, the zones or formations can cave in, slough off or wash out due to the flow of drilling fluid through the wellbore which causes the wellbore to enlarge. This, in turn, can cause the drill string to become stuck as well as a variety of other severe problems. The zones or formations can also be charged with a fluid, e.g., water, which flows into the wellbore making drilling difficult.
In order to solve the problems caused by an unstable subterranean zone or formation, the portion of the wellbore penetrating the zone or formation has heretofore been enlarged and filled with cementitious material. After the cementitious material has set, the wellbore has been drilled through the cementitious material leaving a cementitious sheath in the wellbore for preventing undesired fluid influx, fluid losses, cave-ins, etc. While such techniques have been utilized successfully, they have heretofore required the use of many different tools, the necessity of making many trips in and out of the wellbore, and a great deal of time and expense to complete.
Thus, there is a need for improved methods for stabilizing unstable hydrocarbon producing subterranean zones or formations penetrated by a wellbore which do not require the use of many different tools, numerous drill string and/or work string trips, long delays and the like.